Belt edge sensor and actuator for controlling tracking of such belt

Abstract

A sensor and controller for a belt moving about a path, the sensor and controller including an analog sensor including a medium that changes a characteristic to give a signal that varies continuously with any lateral belt edge position, thus yielding improved resolution of actual belt edge position, and a control mechanism responsive to the changes in characteristics of the medium for more accurate edge position control.

1. Mechanism for controlling lateral tracking of a belt about a path, the mechanism comprising:
 a pressurized-fluid source adapted to provide a flow of fluid under pressure; 
 a sensor unit having a slot therein, the edge of the belt moving about the path arranged in the slot, the sensor unit connected to the pressurized-fluid source, 
 three apertures in the sensor unit disposed so they are selectively closed by the edge of the belt in the slot, the apertures spaced apart in a direction lateral to the movement of the belt about the path, so that the pressure of the fluid varies in proportion to how much of the area of the apertures is blocked by the belt surface, whereby the pressure of the fluid varies in proportion to the lateral position of the belt edge in the slot; 
 a bladder connected to the pressurized-fluid source so that the inflation of the bladder varies according to the pressure of the fluid, 
 a steering roller supporting the belt, the steering roller being rotatable about its longitudinal axis and about a first axis perpendicular to the longitudinal axis, wherein the first axis is substantially parallel to the direction of movement of the belt about the path; 
 a control arm supported on a pivot pin, the control arm engaging the bladder and being operatively connected to the steering roller, so that the rotation of the steering roller about the first axis corresponds to the inflation of the bladder, 
 so that when the lateral position of the belt in the slot changes, the steering roller rotates around the first axis to move the belt laterally. 
 
     
     
       2. The mechanism according to  claim 1  wherein the fluid is air. 
     
     
       3. The mechanism according to  claim 1  wherein the pressure of the fluid is dependent upon the lateral position of the belt relative to a selected nominal lateral position. 
     
     
       4. The mechanism according to  claim 1 , further including a yoke supporting the steering roller and a linkage adapted to move the yoke to rotate the steering roller about the first axis. 
     
     
       5. The mechanism according to  claim 4 , wherein the linkage connects the control arm with the yoke so that, when the bladder inflates, the control arm rotates in corresponding relation to the inflation and moves the linkage to cause the linkage to move the yoke to rotate the steering roller about the first axis.